In the printing and plate making fields, for example, the so-called combination montage techniques including those for making the montages of pictures themselves, pictures and letters, or pictures and marks are so used as to put catalogues, pamphlets and circulars into print.
The combination montages of this kind are carried out, for example, in the following manner. The pieces of some originals clipped in advance are put on a transparent base and a read-only original is prepared. From the read-only original, a negative and a plate-making mask are prepared. Thus, a clipped portion corresponding to a character original, for example, can be formed on the resulting plate-making mask. In this case, a negative of the character original can be obtained by taking the photograph of the character original. The resulting character original negative, read only original negative and the plate-making mask are each put one upon another and are then exposed to light and developed, so that a positive original can be obtained. The resulting positive original is printed on a presensitized printing plate, so that a printing plate is obtained. A printing is carried out by making use of the resulting printing plate, so that a series of the objective pamphlets or circulars are printed.
In the plate-making process for preparing a printing plate by making use of the plate-making block copy, there are the methods for preparing a plate-making mask including, for example, such a method as disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as `Japanese Patent O.P.I. Publication`) No. 63-38941/1988, in which the following procedures are carried out. A mask forming film comprising a support having thereon a pealable mask forming layer is placed on a plate-making block copy; the plate-making block copy is observed through the mask forming film; a slitting kerf is provided onto the portion of the mask-forming layer corespondent to the designated portion of the plate-making block copy; and the portion enclosed by the slitting kerf is separated by pealing it away from the other portions.
The methods for automatically preparing such a slitted mask as described above include, for example, a method such as described in Japanese Utility Model O.P.I. Publication No. 61-157947/1986, in which the following procedures are carried out; the image of an original block is enlarged and projected onto a digitizer; the data of the contours of the enlarged and projected image are obtained by tracing the image contours by making use of a cursor or the like; and the mask-forming film is cut by making use of an XY cutter while keeping it controlled according to the contour data.
An attempt for automating the processes in which a mask for plate-making is prepared by slitting a mask-forming film is described in Japanese Patent O.P.I. Publication No. 2-959/1990. In this technique, however, it is troublesome to remove the slitted portions, because the slitted portions should be removed by hand.
When catalogues, pamphlets and circulars are prepared in color printing and plate making, 3 pieces of plate-making masks are required for color separation and, when the respective plate-making masks are prepared by slitting the mask-forming film, there raise the problems that the removals of the slitted portions of the plate-making masks are liable to be confoundingly forgotten.
It is an object of the invention is to solve the abovedescribed problems and, therefore, to provide a process for preparing a mask for plate-making in which the mask for plate-making can quite readily be obtained by utilizing a thermal transfer technique, and the materials for the mask for plate-making.